This type of personalization first started to be noticed back in April, as discussed in a WebmasterWorld. But that thread lacked actual examples, which the Wiep post provides, as does Ben Murphy in a separate post.

What’s Google doing to make this happen? Google sent this:

What you’re seeing is that we look at the user’s previous query and see how well it intersects with the current query. If it’s significant, we’ll use it to help targeting on the current query. We simply look at what’s in the referring URL (every time you load a web page, the HTTP header includes your previous URL as the “referrer”).